<button mat-icon-button [mat-menu-trigger-for]="fontMenu" matTooltip="更换字体！">
  <mat-icon>format_size</mat-icon>
</button>

<mat-menu class="font-adjuster-menu" #fontMenu="matMenu" x-position="before">
    <mat-slider vertical min="8" max="32" step="1" invert thumbLabel [(ngModel)]="currentFont.fontSize" (ngModelChange)="changeFontSize()"></mat-slider>
</mat-menu>
